In a fiber telecom network, signal transmitted from a transmitter is attenuated along its propagation in the network. The receiver will detect a signal that is weaker than the signal transmitted at the transmitter. The signal may be attenuated because of attenuation loss, return loss, and the like. In other words, when a signal is received by a receiver, the signal may be lower than the level that can be detected by the receiver, although the signal is transmitted with higher power at the transmitter. Accordingly, the transmitter needs to be tested for sufficient transmitting a signal that can be detected by the receiver.
The transmitter is typically tested using a fiber attenuator based on loopback assembly between the transmitter and the receiver to provide the required attenuation between the transmitter and the receiver. The loopback assembly simulates the long fiber connection between the transmitter and the receiver. The loopback assembly traditionally comprises a fiber doped with material to absorb light propagating in the fiber. Thus, a short fiber can gives an effect of a long fiber in the network.
A loopback assembly based on doped fiber is typically expensive. Accordingly, a low cost loopback assembly is desired. In addition, the loopback assembly is required to have the same performance for multimode fibers as well as single mode fibers.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention.